Secondary metabolites of Minutisphaera thailandensis and Hongkongmyces kokensis revealed by LC–QTOF–MS and their antimicrobial and cytotoxic activities

The mycelial extracts of two novel fungal species, Minutisphaera thailandensis and Hongkongmyces kokensis, were investigated for their antimicrobial, cytotoxic, and secondary metabolite profiles to assess their potential as sources of bioactive natural products. LC-QTOF-MS profiling revealed that the mycelial extracts contained a greater diversity of metabolites compared to the culture supernatants. M. thailandensis demonstrated strong antibacterial activity against Bacillus subtilis (MIC = 62.25 µg/mL; inhibition zone = 20.12 ± 0.21 mm), Staphylococcus epidermidis (125.00 µg/mL; 19.32 ± 0.15 mm), and Staphylococcus aureus subsp. aureus (125.00 µg/mL; 19.08 ± 0.12 mm). H. kokensis was active against Pseudomonas aeruginosa (16.45 ± 0.28 mm) and Escherichia coli (16.87 ± 0.36 mm). Both fungi also exhibited antifungal activity against Candida albicans (zones = 13.38-17.29 mm). Fifteen metabolites were identified in the mycelial extract of M. thailandensis while 16 compounds were found in those obtained from H. kokensis. These included alkaloids (norharman, indole-3-carboxylic acid), fatty acid amides (oleamide, stearamide), sphingolipids (phytosphingosine, 3-ketosphinganine), polyketides (chaetochromin), and unsaturated fatty acids (linoleic acid), among others. Both fungi shared 4-hydroxycoumarin, carapin-8(9)-ene, and phytosphingosine, while chaetochromin and 13-epi-12-oxo-phytodienoic acid were unique to H. kokensis. Antimicrobial and cytotoxic activities may be attributed to the presence of bioactive compounds including phytosphingosine, 4-hydroxycoumarin, chaetochromin, linoleic acid, and oleamide, all of which possess reported pharmacological effects. M. thailandensis exhibited stronger cytotoxicity against SW480 (IC₅₀ = 25.11 µg/mL) and A549 (IC₅₀ = 32.68 µg/mL) cell lines than H. kokensis (IC₅₀ = 58.88-63.41 µg/mL), underscoring its therapeutic potential.